The Internet has proven to be a popular and effective method of distributing content. For example, many people access one or more Web sites on the World Wide Web (WWW) each day. Numerous types of content may be accessed using the Internet, such as a Web page, an image file, and streaming video, to name a few examples.
One of the problems facing content delivery over any network, such as the Internet, is the act of defacement. Defacement is the unauthorized modification of content by a third party, such as a “hacker.” Content may be defaced by any unauthorized change, such as any deletion or addition to any portion of the content. Content may be defaced while it is stored at a server or during delivery to a requestor. In some cases, content that has been defaced may be visually different than the original version of the content, e.g., a Website that is defaced may display different images or text. In other cases, content that has been defaced may visually appear the same as the original version of the content, but the defaced version of the content may contain spyware, adware, a computer virus, or other unwanted mechanisms.
One approach for addressing content defacement is to periodically monitor the content via a “content monitor” using a checksum method. To illustrate how a checksum works in one approach, assume that a “content monitor” monitors the content defacement of an origin server. The content monitor may periodically verify that the content obtained from the origin server (“the received content”) has not been defaced by contacting the origin server to obtain a checksum value that is associated with the received content. The content monitor also generates a checksum value for the received content. If the checksum value generated by the content monitor for the received content is different than the checksum value obtained from the origin server that is associated with the received content, then the received content has been defaced.
Using a checksum to detect content defacement via a content monitor has several disadvantages. First, if the amount of time between the first time a content monitor contacts the origin server to obtain a checksum value to verify whether content has been defaced and the next time the content monitor contacts the origin server to obtain a checksum value to verify whether content has been defaced, is too great, then there is a chance if the content is defaced, the defaced content will be delivered to a requestor before the defacement is detected.
Second, if the amount of time between the first time a content monitor contacts the origin server to verify whether content has been defaced and the next time the content monitor contacts the origin server to verify whether content has been defaced, is too small, then the content monitor generates an excessive amount of traffic between the content monitor and the origin server, thereby creating an excessive demand on the resources of both the origin server and the content monitor.
Third, any time that content needs to the updated at the origin site, the mechanism at the content monitor for monitoring the corresponding checksum value at the origin server must be notified, thereby creating additional steps and burdens on the content monitor. Finally, the use of a checksum requires that the content be available prior to the request for that content, so checksums cannot be used for content that is dynamically generated.
Another approach for addressing content defacement involves the use of a watermark. A watermark, as used in this context, is a first piece of content that a second piece of content must contain in order for the second piece of content to be deemed valid, i.e., not defaced. Any content that does not contain the watermark is automatically prevented from being delivered to a requestor of that content. For example, a company may establish a company logo as a watermark, and thereafter only Web pages that include the watermark of the company logo may be delivered to a requestor.
Unfortunately, the use of a watermark to detect content defacement also has several disadvantages. First, content may contain a watermark and still be defaced. For example, the text of a company Web page may be modified, but the Web page may still include the watermark. Also, a watermark may be easily forged by a third party, thereby allowing others to circumvent the use of a watermark to prevent the unauthorized distribution of content to requestors.
Consequently, techniques for protecting a Website against defacement by a third party that do not incur the disadvantages of the above approaches are desirable. The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.